The rates to
convert agricultural and other organic waste into biofuels at low temperatures
are currently too low to be economically competitive. Led by Johannes
Lercher, scientists at DOE's Pacific Northwest
National Laboratory and TU München in Germany developed ways to accelerate the
reaction rates. The solution was forcing a key reaction to occur in the nano-sized
confining pores inside zeolites.

Why It Matters: Shipping organic waste to
biorefineries over distances longer than 50 miles is costly and inefficient. Therefore,
local decentralized conversion processes operating at lower than conventional
temperatures are needed. The critical steps are related to the deconstruction
of the organic waste, as well as to the elimination of oxygen from the
intermediates by acid- base catalysis. This study provided a new approach to boost
the reaction rates, showing a conceptual design to mitigate a critical step
towards realizing decentralized fuel production.

"Theoretically, any municipality could produce its own fuel," said Lercher, Director of
PNNL's Institute for Integrated Catalysis. "We, thus, aimed at designing new
catalytic approaches to lay the foundations for the distributed production of energy
carriers."

Methods: Natural catalysts, or enzymes, provided
the inspiration for the new approach. Mimicking the small pockets in enzymes that
help in accelerating highly specific catalyzed reactions, the team studied
similar-sized cavities in zeolites that hosted hydrated hydronium ions. These
hydronium ions catalyze the dehydration of alcohols, important intermediates in
the conversion of biomass to hydrocarbon fuels.

The
confined space of the zeolite pores forced the reactants together, so the
hydronium ions have a greater chance of being close to an alcohol molecule than
in an unconstrained solution. As the confines also stabilize intermediates, the
reaction rates increase and can be realized at lower temperatures. In this way,
the zeolite-catalyzed reactions were up to 100 times faster.

"The
smaller the cavity, the larger the catalytic effect. We achieved the best
results with diameters far below one nanometer," said Lercher.

What's Next? The researchers at the Institute for Integrated Catalysis
are continuing to uncover the fundamental principles of zeolite catalysis.
Lercher said, "We hope to use these to create the conditions required for
new, decentralized chemical production processes that no longer require
large-scale facilities."